Difference between revisions of "S19: Mystery Machine"

Revision as of 20:10, 23 May 2019

Abstract

This project demonstrates the learning involved in Embedded Systems class to design a self-driving car capable of navigating through terrain and avoiding obstacles in order to reach a destination. The car receives destination GPS coordinates from a custom Android Application and relays back statistics and progress in reaching the target.

Introduction

The objective of this project was to create an autonomous self-driving car which was able to reach the target destination while avoiding obstacles through the terrain. In order to accomplish this, five SJ One boards were used that handled separate functionality of the car:

• Master Controller
• Sensor Controller
• Geo Controller
• Bridge Controller
• Android Application
• Motor and Steering Controller

Team Members & Responsibilities

<Team Picture>
Gitlab Project Link

• Neeraj Dhavale
  • Master Controller [SPOC]
  • Geo Controller [SPOC]

• Sanket Patil
  • Bridge Controller [SPOC]
  • Hardware integration and PCB [SPOC]

• Tarun Chawla
  • Motor and Steering Controller [SPOC]
  • Geo Controller

• Rachit Mathur
  • Motor and Steering Controller
  • Documentation [SPOC]

• Chithambaram Singaravelu Poonkodi
  • Android Application [SPOC]
  • Git Management [SPOC]

• Adithya Baskaran
  • Sensor Controller [SPOC]
  • Hardware and PCB

• Sudarshan Aithal
  • Sensor Controller
  • Hardware integration and PCB

• Sai Kiran
  • Testing

Schedule

Parts List & Cost

Design and Interface

CAN Communication

Hardware Design

System Nodes: SENSOR, MOTOR, GEO CONTROLLER, BRIDGE, MASTER

CAN(Controlled Area Network) is a Broadcast Bus which is heavily used in automotive industry. It defines protocol and hardware interface. It operates in standard baudrates like 100k, 125k, 250k, 500k or 1M bps. CAN uses half duplex communication over differential pair. The number of nodes affect the cable length because more CAN transeives add more capacitance to the bus.

An MCU can be interfaced to CAN bus using CAN transceiver and terminated on each end with 120 ohm resistors. Resisters are used to avoid signal reflexion. CAN is frame based communication where each frame contains ID, length(DLC), and up to 8 data bytes.Message ID field can be 11-bit or 29-bit. Only one transmitter can transmit at a time which has highest priority will go ahead first. Low priority message ID's will back-off.Lower message ID wins i.e zero is dominant.

Each node asserts an ACK if it receives a good frame. Software may or may not accept the frames. If no one ACKS, then the message is retransmitted. Depending on the CAN specifications retransmission error can be send and can eventually lead to "Bus off" state.

DBC File

DBC File

BU_: DBG DRIVER MASTER IO MOTOR SENSOR LIGHT BRIDGE GEO GATEWAY

BO_ 600 SONAR_SENSOR_VALUES: 4 SENSOR
 SG_ SONAR_SENSOR_VALUES_Left_Sensor : 0|9@1+ (1,0) [0|300] "cm" BRIDGE,MASTER
 SG_ SONAR_SENSOR_VALUES_Right_Sensor : 9|9@1+ (1,0) [0|300] "cm" BRIDGE,MASTER
 SG_ SONAR_SENSOR_VALUES_Front_Sensor : 18|9@1+ (1,0) [0|300] "cm" BRIDGE,MASTER

BO_ 601 DEMO_IR_SENSOR: 6 SENSOR
 SG_ LEFT_SENSOR : 0|16@1+ (1,0) [0|0] "LEFT_VALUES" MASTER
 SG_ RIGHT_SENSOR : 16|16@1+ (1,0) [0|0] "RIGHT_VALUES" MASTER
 SG_ FRONT_SENSOR : 32|16@1+ (1,0) [0|0] "FRONT_VALUES" MASTER

BO_ 602 SONAR_SENSOR_THRESHOLD: 3 BRIDGE
 SG_ UPDATE_THRESHOLD_VALUE_Left : 0|8@1+ (1,0) [0|0] "cm" MASTER
 SG_ UPDATE_THRESHOLD_VALUE_Right : 8|8@1+ (1,0) [0|0] "cm" MASTER
 SG_ UPDATE_THRESHOLD_VALUE_Front : 16|8@1+ (1,0) [0|0] "cm" MASTER

BO_ 603 STEER_CMD: 1 SENSOR
 SG_ SENSOR_STEER_DIRECTION : 0|8@1+ (1,0) [0|0] "DIRECTION" MASTER,BRIDGE

BO_ 604 SONAR_REVERSE_SENSOR: 2 SENSOR
 SG_ SONAR_REVERSE_SENSOR_value : 0|9@1+ (1,0) [0|300] "cm" BRIDGE,MASTER

BO_ 700 MOTOR_SPEED: 1 MASTER 
 SG_ MOTOR_SPEED_speed_in_mps : 0|8@1+ (0.01,0) [0|2] "mps" MOTOR,BRIDGE

BO_ 701 STEER_DIRECTION: 2 MASTER
 SG_ STEER_DIRECTION_ANGLE : 0|16@1- (1,0) [0|0] "ANGLE" MOTOR,BRIDGE

BO_ 702 DEMO_STEER_DIRECTION: 2 MASTER
 SG_ STEER_DUTY_CYCLE_VAL : 0|8@1+ (0.01,0) [0|0] "DUTY_CYCLE" MOTOR,BRIDGE

BO_ 703 DEMO_MOTOR_SPEED: 2 MASTER
 SG_ MOTOR_SPEED_DUTY_CYCLE : 0|8@1- (1,0) [-127|127] "DUTY_CYCLE" MOTOR,BRIDGE

BO_ 704 MOTOR_FLAG: 1 MOTOR
 SG_ REVERSE_FLAG : 0|8@1+ (1,0) [0|0] "MOTOR_FLAG" MASTER,BRIDGE

BO_ 740 COMPASS_DATA: 2 GEO
 SG_ COMPASS_HEADING_ANGLE : 0|9@1+ (1,0) [0|0] "DEGREES" MASTER,BRIDGE

BO_ 750 GPS_DATA: 8 GEO
 SG_ GPS_LOCK : 0|1@1- (1,0) [0|0] "" MASTER,BRIDGE
 SG_ CURRENT_GPS_COORDINATES_X : 8|28@1- (0.000001,0) [36.000000|38.000000] "" MASTER,BRIDGE
 SG_ CURRENT_GPS_COORDINATES_Y : 36|28@1- (0.000001,0) [-122.000000|-120.000000] "" MASTER,BRIDGE

BO_ 751 TELEMETRY: 8 GEO
 SG_ DISTANCE_TO_DEST : 0|8@1+ (1,0) [0|0] "" MASTER,BRIDGE

BO_ 790 MASTER_HEARTBEAT: 1 MASTER
 SG_ HEART_BEAT : 0|8@1+ (1,0) [0|0] "MASTER_HEARTBEAT" BRIDGE

BO_ 800 APP_CMD: 2 BRIDGE
 SG_ START_COMMAND : 0|8@1+ (1,0) [0|0] "" MASTER
 SG_ ABORT_COMMAND : 8|8@1+ (1,0) [0|0] "" MASTER

BO_ 805 WHEEL_ENCODER: 1 MOTOR
 SG_ WHEEL_ENCODER_data : 0|7@1+ (1,0) [0|0] "" MASTER,BRIDGE

BO_ 810 APP_DESTINATION_GPS: 8 BRIDGE
 SG_ DEST_GPS_COORDINATES_X : 0|28@1+ (0.000001,0) [0|0] "" GEO
 SG_ DEST_GPS_COORDINATES_Y : 28|28@1+ (0.000001,0) [0|0] "" GEO

BO_ 909 SENSOR_TRIGGER: 1 SENSOR
 SG_ SENSOR_TRIGGER_Trigger_status : 0|1@1+ (1,0) [0|1] "" BRIDGE

BO_ 908 SENSOR_INIT: 1 SENSOR
 SG_ SENSOR_INIT_init_Status : 0|1@1+ (1,0) [0|1] "" BRIDGE

BO_ 910 SENSOR_TIMEOUT: 1 SENSOR
 SG_ SENSOR_TIMEOUT_left : 0|1@1+ (1,0) [0|1] "" BRIDGE
 SG_ SENSOR_TIMEOUT_center : 2|1@1+ (1,0) [0|1] "" BRIDGE
 SG_ SENSOR_TIMEOUT_right : 3|1@1+ (1,0) [0|1] "" BRIDGE
 SG_ SENSOR_TIMEOUT_reverse : 4|1@1+ (1,0) [0|1] "" BRIDGE

BO_ 911 LEFT_SENSOR_ECHO_TIME: 2 SENSOR
 SG_ LEFT_SENSOR_ECHO_TIME_left_calculation_time : 0|16@1+ (1,0) [0|0] "us" BRIDGE

BO_ 912 RIGHT_SENSOR_ECHO_TIME: 2 SENSOR
 SG_ RIGHT_SENSOR_ECHO_TIME_right_calculation_time : 0|16@1+ (1,0) [0|0] "us" BRIDGE

BO_ 913 CENTER_SENSOR_ECHO_TIME: 2 SENSOR
 SG_ CENTER_SENSOR_ECHO_TIME_center_calculation_time : 0|16@1+ (1,0) [0|0] "us" BRIDGE

BO_ 917 REVERSE_SENSOR_ECHO_TIME: 2 SENSOR
 SG_ REVERSE_SENSOR_ECHO_TIME_reverse_calculation_time : 0|16@1+ (1,0) [0|0] "us" BRIDGE

BO_ 914 TOTAL_SENSOR_CALCULATION_TIME: 4 SENSOR
 SG_ TOTAL_SENSOR_CALCULATION_TIME_total_time : 0|32@1+ (1,0) [0|0] "us" BRIDGE

BO_ 915 PERIODIC_SCHEDULER_INIT: 1 SENSOR
 SG_ PERIODIC_SCHEDULER_INIT_scheduler_init_status : 0|1@1+ (1,0) [0|1] "" BRIDGE

BO_ 916 DBG_SENSOR_THRESHOLD: 4 MASTER
 SG_ THRESHOLD_VALUE_Left : 0|8@1+ (1,0) [0|0] "SONAR_DBG" BRIDGE
 SG_ THRESHOLD_VALUE_Right : 8|8@1+ (1,0) [0|0] "SONAR_DBG" BRIDGE
 SG_ THRESHOLD_VALUE_Front : 16|8@1+ (1,0) [0|0] "SONAR_DBG" BRIDGE
 SG_ THRESHOLD_VALUE_Reverse : 24|8@1+ (1,0) [0|0] "SONAR_DBG" BRIDGE

BO_ 921 SPEED_CMPS: 1 MOTOR
 SG_ SPEED_CMPS_car : 0|7@1+ (1,0) [0|0] "CAR SPEED IN CM/S" MASTER,BRIDGE

BO_ 926 MOTOR_DUTY: 1 MOTOR
 SG_ MOTOR_DUTY_CYCLE : 0|7@1+ (1,0) [0|1] "" MASTER,BRIDGE

BO_ 922 ROTATIONS_PER_SECOND: 1 MOTOR
 SG_ ROTATIONS_PER_SECOND_WHEELS : 0|7@1+ (1,0) [0|0] "CAR SPEED IN ROTATIONS/SECOND" MASTER,BRIDGE

BO_ 923 STEER_DUTY_LEFT: 1 MOTOR
 SG_ DUTY_CYCLE_LEFT : 0|7@1+ (1,0) [0|1] "" MASTER,BRIDGE

BO_ 924 STEER_DUTY_RIGHT: 1 MOTOR
 SG_ DUTY_CYCLE_RIGHT : 0|7@1+ (1,0) [0|1] "" MASTER,BRIDGE

BO_ 925 STEER_DUTY_CENTRE: 1 MOTOR
 SG_ DUTY_CYCLE_CENTRE : 0|7@1+ (1,0) [0|1] "" MASTER,BRIDGE

Sensor ECU

Sensor ECU

Ultrasonic sensors are great tools to measure distance without actual contact. Basic principal of ultrasonic distance measurement is based on ECHO and Trigger pins. Trigger pin is used to send the sonar wave from ECHO. ECHO goes high as soon as it sends Sonar wave. Once it receives the wave the ECHO pin will go low. We will measure this ECHO HIGH period and use to calculate the distance.

Hardware Design

For object detection we are ultrasonic sensors , Three in the front (LEFT, RIGHT and CENTER) and one behind to measure the distance of each object if present in front of the sensors general direction. The sensor presented each have a specific threshold beyond which the car is supposed to react and avoid obstacles by altering the direction of travel.

Hardware Interface

The trigger pin is common since all the sensors are activated at the same time. Echo in are individual and processed in parallel.The CAN connections are same as every other module.

In order to raise the sensor at a height decent enough to detect obstacles directly ahead of the RC car, we designed custom 3D printed mounts for all the sensors. These stand provided a rigid support for these sensors as well as ensured that the sensors would survive an accidental head-on crash.

Screenshots of these custom mounts can be seen along side.

Software Design

Sensors are calculated over in periodic functions and sent to master module by use of the CAN connections between them.

Implementation

In 100 Hz, Through the GPIO pin TRIGGER signal is sent and waits fro the ECHO signal to be created . If the timeout function runs out before the Echo completes the minimum distance is said to be obstacle free. If not the time taken for the signal to go high and then low is calculated with respect to speed of sound.

In 20 Hz, the data is sent through the CAN messages from the sensor module to the master and Bridge module.

Pseudo Code:

void 10hz_task(int count){
    initialize the sensors;
    Reset_flags;
    Trigger each sensors;
    calculate the distance;
    if( timeout){
          capture current value;
          set flags;
    }
    send distance values over can;
}

Technical Challenges

Initially we went with sharp 2yoa21 IR sensor to obtain better precision. But the range of the sensor was 48cm which was not reliable distance for obstacle detection. We upgraded to an Ultrasonic sensor which had trouble with echo reception due to faulty firmware code. <Bullet or Headings of a module>

Unreliable sonor sensors

We upgraded to an Ultrasonic sensor HC-SR04 which had a better range of around 200cm with reliable precision. Also we faced another problem with Ultrasonic Sensor. There was some chinese firmware code in the ultrasonic sensor due to which echo pin did not receive the signal for a long duration of time. We had 3 Ultrasonic sensors working together and each received other's echo signals sometimes due to reflection. To solve the reflection problem, We elevated the sensor position and changed the direction of the sensor. To solve the faulty firmware, we introduced a timeout of 8ms in the code, until the timeout, if we don't receive the echo pulse, it will give a default distance of 110cm.

Motor ECU

Motor ECU

DC Motor

Our car arrived with an in-built Electronic Speed Controller(ESC) that was responsible for controlling the steering servo motor and running the DC motor attached to the rear wheels.Along with the motor control, the ESC was also embedded with a receiver for the remote control that shipped with the car.

We realized that the ESC could not be tapped into by providing an external signal to the pin-heads available on the exterior. This external signal from a function generator gave unsatisfactory results when passed through the ESC but we did conclude the optimal frequencies at which both the motors worked satisfactorily.

A motor controller module was used for driving the DC motor. We experimented with the frequency input to the motor driver to run the motor at and found that it operated best at a high frequency of 4KHz,

Servo Motor

The servo motor was connected directly to the GPIO ports of the SJ One board.

After applying an external PWM signal to the servo, we concluded that the servo motor was designed to work smoothly on 80Hz frequency. Accordingly, accurate values of the duty cycle were noted to get precise angles of the steering.

Encoder Sensor

As part of speed feedback, we designed a custom encoder wheel between an encoder sensor mounted on the rear wheel shaft.

The wheel had a finite number of spokes which when intercepted the encoder receiver, a value was read at the falling edge of interrupt signifying one wheel rotation.

These detected number of rotations were passed into a formula that calculated the wheel speed in cm/s.

As part of the feedback, if the calculated wheel speed was not equivalent to the constant speed the PWM duty cycle was either increased or decreased to match the target.

A special scenario was also taken into consideration. If the speed of the wheel continued to remain zero after increasing the PWM duty cycle to the Maximum defined limit, then a reverse logic was called.

This case helped us in overcoming obstacles that were underneath the car and were initially not detected by the sensors.

Hardware Design

Software Design

<List the code modules that are being called periodically.>

Technical Challenges

• The primary challenge in the motor module was tapping into the ESC of the car but that was soon replaced by a Motor Driver module.

• While trying to run the motor driver module at a lower frequency of around 500Hz, we faced an issue of 'heat lock' where after 10 minutes the motor driver module would cut off the supply to the DC motor due to excessive heating. To fix this, we concluded that the motor driver module that we ordered worked best at a higher frequency upwards of 1KHz.

• We also learned about the limitation of the SJ One board in providing two PWM signals at different frequencies. To solve this, we temporarily attached the steering control with the Master Controller.

Geographical Controller

Geographical ECU

The Geographical controller is responisable for navigating the car in the direction of destination selected in the android app. It uses GPS module which gives the current location of the car and compass module for getting the heading angle of the car. After a destination location is selected in the android app, using the shortest path algorithm, the app generates a pirticular number of check points. These check points are then send to bridge controller. Now Bridge controller sends one check point at a time to the Geographical controller. Geo controller uses its current location and the destination location(check point) to calculate the bearing angle and the distance to the destination. Subsequently, heading angle and bearing angle are used to determine the angle that the car should turn, and sent to the master module. On reaching destination, the car will stop.

Hardware Design

GPS Module

Two modules are used in Geograpgical controller: GPS and Compass

GPS

Ublox NEO-7M GPS Module is used for detecting the location of the car. This module returns NMEA string which need to be parsed to get lock, latitude and longitude values from the module. To use the GPS string first we need to get lock. Values read are valid only if we get GPS lock.

COMPASS

MPU-9150

The MPU-9150 is first integrated 9-axis MotionTracking device that combines a 3-axis MEMS gyroscope, a 3-axis MEMS accelerometer, a 3-axis MEMS magnetometer and a Digital Motion Processor hardware accelerator engine. The MPU9150’s 9-axis MotionFusion combines acceleration and rotational motion plus heading information into a single data stream for the application.

The MPU-9150 features three 16-bit analog-to-digital converters (ADCs) for digitizing the gyroscope outputs, three 16-bit ADCs for digitizing the accelerometer outputs and three 13-bit ADCs for digitizing the magnetometer outputs. For precision tracking of both fast and slow motions, the parts feature a userprogrammable gyroscope full-scale range of ±250, ±500, ±1000, and ±2000°/sec (dps), a user programmable accelerometer full-scale range of ±2g, ±4g, ±8g, and ±16g, and a magnetometer full-scale range of ±1200µT.

Communication with all registers of the device is performed using I2C at 400 kHz.

Hardware Design

GPS module is interface over UART:

Compass module is interface over I2C:

Software Design

<List the code modules that are being called periodically.>

Flowchart

Algorithm

Implementation

Formulae:

Current latitude and longitude position can be obtained form GPS module and destination latitude and longitude position should be determined from CAN message sent by bridge module. In order to compute the angle the car need to turn to reach destination can be computed using bearing angle and heading angle.

Bearing Angle - is the angle between the direction towards destination from the current location with respect to north.

Heading Angle The angle given by the compass. This is the angle with respect to north. Which is used to know the heading direction of car with respect to north.

Angle to turn

We need to compute the angle that the car has to turn from its current direction towards the destination, from the obtained bearing angle(angle at which the car should go with respect to north to reach the destination) and heading angle (angle at which our car is going currently with respect to north).

we need to compute the angle that the car has to turn from its current direction towards destination, from the obtained bearing angle and heading angle.

Angle to turn = Heading angle - Bearing angle

Distance Calculation

Technical Challenges

<Bullet or Headings of a module>

Unreliable GPS lock

<Problem Summary> <Problem Resolution>

Communication Bridge Controller & LCD

Bridge ECU

MQTT Protocol

MQTT protocol was chosen as the communication protocol between the android application since it is very light weight and is designed ideally for IOT devices.

For establishing the connection via MQTT a MQTT server has to be created and run. The clients can connect to that server. Multiple clients can connect to the server and share data between them

Message Passing

The data transfer in MQTT is done via topic scheme, where when a client has to send a message it has to publish the message with a topic. The client can subscribe to topics (which is essentially string). Whenever someone publishes a message in a topic every client subscribed to that topic will receive the message. The clients are not directly connected but in turn connected via the MQTT server

Server Setup

The RC car is equipped with a wifi-module. The wifi modules run a MQTT server to which it connects itself to and the mobile application also connects to wifi module and establishes a connection to the MQTT server. The communication happens by a set of predefined topics which each of the clients listen to and publish their message.

Hardware Design

The message inside in each topic is again formatted as below: “<COMMAND:value1|value2|value3”>

Here the COMMAND can be the type of message like “GO”, “COMPASS”, “RPS”(Rotation per second), “SPEED” etc. Each of these messages can have n number of values in them depending upon the type. For example the “COMPASS” type has only one value while the “SENSOR” has 4 values - one for each sensor in the car.

Software Design

<List the code modules that are being called periodically.>

Technical Challenges

<Bullet or Headings of a module>

Insane Bug

<Problem Summary> <Problem Resolution>

Master Module

Master ECU

Master Controller

The master controller is responsible for the handling motion of the car. The master controller decides how the car will move based on inputs from all the other ECUs. The master first waits to receive the start command from the Android app via Bridge ECU. When the app sends “START Command” the master controller takes the values of ultrasonic sensors from the Sensor Controller, also the master takes the direction angles from the Geo controller. The master controller first calculates if there are any obstacles, it will avoid those obstacles by giving out motor speed values to the motor controller and steer accordingly. Then the master starts following the steer instructions provided by the Geo Controller. The obstacle avoidance algorithm preempts the GEO controller navigation directions.

Obstacle Avoidance

The obstacle avoidance algorithm implemented is simple. The master controller receives values of the ultrasonic sensors from the Sensor Controller. The values which are distances in centimeters are received from the front, left, right and back sensor. When the car is supposed to move forward the master checks the values of the front, left and right sensors and checks if all the values are above the threshold.

Hardware Design

Software Design

The pseudocode of steering is as below:

if(left sensor < threshold){
    STEER RIGHT();
}
if(right sensor < threshold){
    STEER LEFT();
}
else{
    Follow GPS_directions();
}

The pseudocode for speed controlling as below:

if(front_sensor < threshold){
    REVERSE();
}
else if(left_sensor && right_sensor < threshold){
    REVERSE();
}

Technical Challenges

<Bullet or Headings of a module>

Improper Unit Testing

<Problem Summary> <Problem Resolution>

Mobile Application

Mobile Application

The Android application allows the user to interface with the RC car. The connection between the car and the mobile is established via MQTT protocol. The app requires that the mobile is connected to the Mystery machine wifi that is hosted by the wifi modules mounted on the car. Then the app automatically connects to the car via the MQTT broker.

Once connected the app takes part in a two-way communication that allows it to send commands to the car and to receive information from the car.

Since the mqtt client does not provide the connection details of the other clients that is connected to it, we are using a heartbeat message from the wifi module to ensure that the Android application can know the connection status of the car.

Transmission

• App sends the GO and STOP commands that starts and stops the motor accordingly.
• The messages are <GO0> for stop and <GO1> for start
• Sends the destination coordinates can be set by the user in the Android application by placing the destination marker on the Google Maps in the app. The marker can be moved by clicking on the map where ever the user wishes to place the destination for the car and the destination can be send by use of the destination send button
• The message is <GPS:latitude|longitude>

Reception

• The current speed of the car
• The direction the car is heading
• The direction of the destination
• RPS of the motor
• Sensor values
• Current location of the car

Software Design

Technical Challenges and Solutions

• Integrating the map onto the app was an issue.
• Since the application was designed with fragments and the map view integration was tricky.
• Solved it by converting everything into fragment including the map and a common fragment container.

Improvements

The app now connects directly to the car via the wifi hosted by the car. It can be improved by connecting the car to the cloud and there by the app can connect to the car from any where by connecting to the cloud.

Conclusion

<Organized summary of the project>

<What did you learn?>

Project Video

Project Source Code

Advise for Future Students

<Bullet points and discussion>

Acknowledgement

References